1. Field of the Invention
This invention relates to a recombinant Marek's disease virus. More particularly, the present invention is concerned with a recombinant Marek's disease virus comprising an attenuated Marek's disease virus and a foreign gene which does not inherently exist in the attenuated Marek's virus. The recombinant virus of the present invention can advantageously be used as an active ingredient for a multifunctional live vaccine, namely a live vaccine having not only the anti-genicity and immunogenicity of the Marek's disease virus but also the properties ascribed to the foreign gene. Further, since the suitable host cell for the recombinant virus of the present invention is an avian cell which is available in a large quantity and not expensive, the recombinant virus of the present invention can be produced efficiently on a commercial scale at low cost.
2. Discussion of Related Art
Marek's disease is a viral lymphoproliferative disease which is highly contagious and spreads mainly in young chicken flocks. The disease had been recognized as a kind of lymphoid leukemia, but in 1961 Biggs distinguished this disease from leukemia of chicken and named it "Marek's disease" after the the name of the discoverer, Marek, who was first to report this disease.
The Marek's disease virus is a DNA virus having an envelope and is classified into Gallid herpes-virus 1 or Gallid herpes-virus 2 belonging to the subfamily Gammaherpesvirinae in the family Herpes-viridae (Intervirology, Vol. 17, pp. 47-51, S. Kerger, 1982). The diameter of a mature virus particle of this virus, including an envelope, is about 150 to 180 nm. The virus is comprised of an envelope and a nucleocapsid contained therein. The nucleocapsid has a shape of regular icosahedron having a diameter of about 100 nm. In the center of the nucleocapsid, there exists a nucleoid having a toroidal structure of a diameter of about 50 to 60 nm and containing a straight double-stranded DNA having a molecular weight of about 1.0.times.10.sup.8. The virus attacks 12 to 20-week age chicks to cause a paresis and a spastic or atonic paralysis due to the lesion of nerves, and causes tumors. The Marek's disease prevails quickly and the mortality by this disease is extremely high. Therefore, the economical damage caused by this disease is very large. In order to prevent this disease, a Marek's disease virus live vaccine has broadly been used in the field of the poultry raising for about 10 years. The Marek's disease virus is classified into the following three serotypes according to the results of a fluoroimmunoassay, an agar gel immunodiffusion and a virus neutralization test (Advances in Virus Research, Vol. 30, pp. 225-277, Academic Press, INC., 1985; and The Herpesvirus, Vol. 1, ed. B. Roizman, pp. 333-431, Plenum Press, 1982).
Type I: a virulent strain of Marek's disease virus (hereinafter referred to as "MDV") which is pathogenic and tumourigenic to chickens and causes various symptoms in chickens, and an attenuated strain of the above-mentioned virulent MDV, which is nonpathogenic and obtained by artificial mutation of the above-mentioned virulent strain cultured in a cell culture in vitro;
Type II: a wild attenuated strain of Marek's disease virus; and
Type III: a herpesvirus of turkeys (hereinafter referred to as "HVT") nonpathogenic to chickens.
The term "attenuated Marek's disease virus" used herein means any one of the attenuated MDV strain of Type I, the wild attenuated MDV strain of Type II, and the HVT of Type III.
Heretofore, various virus vectors have been reported since around 1979. For example, reference may be made to Nature (London), 277, 108-114 (1979); ibid., 278, 35-40 (1979), in which the production of rabbit .beta.-globin by the use of an SV40 vector is reported. In 1980, the World Health Organization (WHO) declared, in the general meeting, the success in extermination of the smallpox in the world and counseled the abolishment of vaccination because of the danger that some persons who received vaccination are killed due to its adverse effect. Since then, with respect to possible utilities of vaccinia virus in other fields, many studies have been made. For example, the use of the vaccinia virus as a cloning vector and an expression vector has been studied and reported [Proceedings of The National Academy of Sciences, U.S.A., 79, 4927-4931 (1982); and ibid., 79, 7415-7419 (1982)]. Thereafter, the Special Advisory Group in WHO proposed a project for promoting the research of a recombinant vaccine by the use of a virus vector derived from a vaccinia virus etc. [Nature (London), 312, 299 (1984)]. Since the above-mentioned declaration and proposal of WHO, fundamental study on and development of various virus vectors have broadly been made [Virus, 36, 1-41 (1986) and ibid., 37, 1-40 (1987)]. Heretofore, it has been reported that, for example, a papillomavirus, a polyomavirus, an adenovirus, a vaccinia virus, a retrovirus, a baculovirus, a parvovirus, a cauliflower mosaic virus and a tobacco mosaic virus can be used as a cloning vector or an expression vector for a foreign gene. With respect to the production of a useful substance by the use of a virus vector as mentioned above, reference may be made to, for example, the following publications:
Use of an attenuated vaccinia virus vector: European Patent Application Publication Specification No. 83286 (production of various antigens), PCT Patent Application Publication No. WO84/02077 (production of various antigens), Japanese Patent Application Laid-Open Specification No. 61-289888 (production of an antigen of a malarial parasite), Japanese Patent Application Laid-Open Specification No. 62-44178 (production of a hepatitis B virus surface antigen), Japanese Patent Application Laid-Open Specification No. 62-151186 (production of a feline leukemia virus antigen), Japanese Patent Application Laid-Open Specification No. 62-294698 (production of a melanoma antigen), Japanese Translation Publication No. 63-500003 of PCT Patent Application (production of .gamma.-interferon) and Japanese Translation Publication No. 63-500005 of PCT Patent Application (production of human interleukin 2);
Use of a nonpathogenic adenovirus vector: PCT Patent Application Publication No. WO83/02393 (production of a polyomavirus antigen) and Japanese Patent application Laid-Open Specification No. 63-12296 (production of a protein such as C-peptide);
Use of a bovine rotavirus vector: PCT Patent Application Publication No. W085/00184 (production of a human rotavirus antigen);
Use of a virulent herpes simplex virus type 1 vector: Japanese Patent Application Laid-Open Specification No. 61-1390 (production of a hepatitis B virus surface antigen) and Japanese Patent Application Laid-Open Specification No. 62-257385 (preparation of an attenuated recombinant virus comprising virulent herpes simplex viruses types 1 and 2);
Use of a long terminal repeat (LTR) vector derived from a retrovirus: Japanese Translation Publication No. 61-502932 of PCT Patent Application (amplification of the production of a tumor specific antigen);
Use of an attenuated varicella virus vector: Japanese Patent Application Laid-Open Specification No. 63-12277 (production of an Epstein-Barr virus antigen); and
Use of a tobacco mosaic virus vector: Japanese Patent Application Laid-Open Specification No. 63-14693 (transformation of a higher plant cell).
However, the above-mentioned techniques are still only at the stage of experiment with respect to production of biological preparations, including vaccines, because not only do not these conventional techniques give satisfactory yields and purities of intended products, but also the safety and effect of the products on a human being, a domestic fowl, a domestic animal and a pet have not been confirmed. Therefore, any biological preparations produced by using a conventional virus vector have not yet been approved officially and put to practical use. For example, with respect to a vaccinia virus vector, the vector can be used for producing various useful substances as mentioned above. However, the vaccinia virus vector is disadvantageous in that the vector is inherently neuro-pathogenic and therefore has the danger of causing serious adverse effects, e.g., the danger of induction of postvaccinal encephalitis. Accordingly, the safety of the vaccinia virus vector and product obtained by means of the vector is uncertain. Further, it should be noted that since there are not a few persons and animals that have already acquired the immunity against the vaccinia virus and have antibodies against the virus, when the recombinant vaccinia virus containing a foreign gene is administered as a live vaccine to such a person or animal, the multiplication of the recombinant vaccinia virus, that is, the multiplication of the foreign gene, in a human or animal body, which is required to attain a sufficient effect of immunization, is disadvantageously suppressed or prevented. Therefore, it is not always expected to attain the desired effect of the recombinant virus as a multifunctional live vaccine having not only the antigenicity and immunogenicity of the vaccinia virus but also the properties ascribed to the foreign gene. In other words, the subjects to whom the administration of the recombinant vaccinia virus is effective are limited and, therefore, such a recombinant vaccinia virus containing the foreign gene cannot always be used as an effective live vaccine.
Further, there has also been tentatively conducted the production of various substances by means of a recombinant virus comprising, as a vector, the genome of baculovirus, e.g., of Autographa california nuclear polyhedrosis virus which is capable of infecting lepidopteran insects [Bio/Technology, Vol. 8, No. 6, pp. 47-55, (1988)]. Examples of substances produced by the recombinant baculovirus include about 35 kinds of antigens and enzymes, for example, human interferons .alpha. and .beta., human interleukin 2, parainfluenza virus hemagglutinin-neuraminidase, influenza virus hamagglutinin, various antigens of AIDS virus, hepatitis B virus surface antigen, Escherichia coli .beta.-galactosidase and the like. However, the production of the above-mentioned products using the baculovirus must be conducted in a limited type of culture host, namely an insect cell, and the safety and effect of the products on humans or animals have not yet been confirmed. Further, the suitability of the vector for use in producing the desired substances on a commercial scale has not been considered. Moreover, since the host cell of the above-mentioned recombinant vaculovirus is an insect cell which is not available in a large quantity and is expensive, the desired substances cannot be produced by the recombinant vaculovirus on a commercial scale at low cost.
From the foregoing, it is apparent that a recombinant virus which can be safely produced on a large scale and can advantageously be used as an active ingredient for a multifunctional live vaccine with safety has heretofore not been developed, and it has been earnestly desired to overcome the above-mentioned disadvantages of the conventional recombinant virus vectors.